1) Fungus 
Pythium is a genus of parasitic oomycotes. Most species are plant parasites, but Pythium insidiosum is an important pathogen of animals. They were formerly classified as fungi; the feet of the fungus gnat are frequently a vector for their transmission. ==Morphology== ==Ecological importance== Pythium-induced root rot is a common crop disease. When...
a genus of destructive root-parasitic fungi of the family Pythiaceae (phylum Oomycota, kingdom Chromista), having filamentous sporangia, ...
A mastigomycotina genus of destructive root-parasitic fungi including forms that cause damping-off of seedlings. ... (12 Dec 1998) ... 
[n] - any fungus of the genus Pythium
noun any fungus of the genus Pythium